The present invention relates to the fields of downhole oil, gas, and/or geothermal exploration and more particularly to piston assemblies for actuating downhole tools. There exists in the art a variety of downhole tools comprising piston assemblies configured to actuate downhole tools to protrude and retract. One such downhole tool may be a directional steering mechanism. In directional drilling operations, a piston may extend a pad that contacts a formation and causes the drill string to move in a direction. Other such tools include expandable tools configured to enlarge the diameter of a wellbore and/or stabilize a drill string. The expandable tools may contain arms or blades which extend from the sides of the drill string and contact the formation. Examples from the prior art of such piston assemblies used in downhole tools are given below.
U.S. Patent Publication No. 2010/0071962 to Beuershausen, which is herein incorporated by reference for all that it contains, discloses a drill bit that includes at least one blade profile having a side section and an adjustable pad on the side section that is configured to extend from the side section to cause the drill bit to alter a drilling direction when the drill bit is used to drill a wellbore.
U.S. Patent Publication No. 2010/0139980 to Neves et al., which is herein incorporated by reference for all that it contains, discloses a ball piston steering device and methods for use of ball piston devices. One aspect of the invention includes: a sleeve in fluid communication with a fluid source and a ball received within the sleeve. The ball is movable within the sleeve from a recessed position and an extended position.
U.S. Patent Publication No. 2006/0157283 to Hart, which is herein incorporated by reference for all that it contains, discloses a bias unit comprising at least one bias pad moveable by a piston between retracted and extended positions wherein the piston is of non-circular effective cross-sectional shape.
U.S. Patent Publication No. 2004/0206549 to Dewey et al., which is herein incorporated by reference for all that it contains, discloses a downhole tool that functions as an underreamer or as a stabilizer in an underrreamed borehole. The tool includes one or more moveable arms disposed within a body having a flowbore therethrough in fluid communication with the wellbore annulus. The tool alternates between collapsed and expanded positions in response to differential fluid pressure between the flowbore and the wellbore annulus. In one embodiment, the tool moves automatically in response to differential pressure. In a second embodiment, the tool must be selectively actuated before it is moveable. The tool may include borehole engaging pads that comprise cutting structure or wear structures or both, depending upon the function of the tool.
Despite the advancements as shown in the prior art, it is believed that there is still a need to develop improved piston assemblies used in downhole drill strings.